Hydrogen exchange methods developed in this lab are being used to study structure, structure change, and breathing behavior in a number of biological macromolecules. Individual structure changes in hemoglobin are being separately identified and characterized. Previous studies of structure and structure change in some vertebrate rhodopsins are being extended to bacteriorhodopsin. The breathing behavior of polynucleotides is being further probed in hydrogen exchange studies of DNA cross-linked covalently with nitrogen mustards and non-covalently with actinomycin. BIBLIOGRAPHIC REFERENCES: S.W. Englander. Measurement of structure and free energy changes by difference hydrogen exchange. Annals N.Y. Acad. Sci., 244, 10 (1975). H. Teitelbaum and S.W. Englander. The major open state in native polynucleotides. I. Hydrogen exchange study of adenine-containing double helices J. Mol. Biol. 92, 55 (1975).